Surplus munitions present a problem to the US military. Current budget constraints force the US military to prioritize its spending while effectively defending the interests of the United States. Defense budgets are further tightened because aging and surplus munitions must be guarded and stored. The US military regularly destroys a significant amount of its surplus munitions each year in order to meet its fiscal challenge. It also destroys a significant amount of munitions each year due to deterioration and obsolescence.
In the past, munitions stocks have been disposed of by open burn/open detonation (OBOD) methods—the most inexpensive and technologically simple disposal methods available. Although such methods can effectively destroy munitions, they fail to meet the challenge of minimizing waste by-products in a cost effective manner. Furthermore, such methods of disposal are undesirable from an environmental point of view because they contribute to the pollution of the environment. For example, OBOD technology produces relatively high levels of NOx, acidic gases, particulates, and metal waste. Incomplete combustion products can also leach into the soil and contaminate ground water from the burning pits used for open burn methods. The surrounding soil and ground water must often be remediated after OBOD to meet environmental guidelines. Conventional incineration methods can also be used to destroy munitions, but they require a relatively large amount of fuel. They also produce a significant amount of gaseous effluent that must be treated to remove undesirable components before it can be released into the atmosphere. Thus, OBOD and incineration methods for disposing of munitions become impractical owing to increasingly stringent federal and state environmental protection regulations.
Various other incineration processes have been used to dispose of munitions including plasma arc, molten-metal/molten-salt baths, dilution in fuel stocks, and charge transfer complex oxidation technologies. These various other processes effectively destroy the excess munitions but fail to meet the R3 challenge (recovery, reclamation, and reuse) of recovering energetic materials in a cost-effective manner to minimize waste generation. Further, destructive technologies prevent explosive component recovery and conversion of the excess munitions into unusable waste streams such as CO2, N2, and NOx stream, as well as solid waste streams.
Another disposal technology advanced to dispose of unwanted munitions utilizes the high temperatures generated in a plasma arc to decompose the munitions. This process avoids the problems of site remediation because it completely decomposes all chemical compounds in the plasma. Hypothetically, no partially decomposed compounds remain. Everything fed to the plasma chamber fully decomposes into oxidized gases such as CO2, and NOx. This process, however, is not only technically difficult and power intensive, but the plasma arc also creates many of the same gaseous waste problems as OB/OD. Unless excess oxygen is injected into the chamber, the plasma chamber will incompletely burn the munitions. The presence of excess combustion oxygen exacerbates the generation of nitrous oxides. The presence of chlorine or fluorine in the binders has the potential of generating dioxins or furans. In addition, the chambers cannot process loaded munitions due to the delicate nature of the refractories. Consequently, plasma arc technologies offer no cost or processing advantages over OB/OD with conventional munitions and work best for the destruction of extremely toxic or dangerous compounds such as chemical and biological weapons.
Further, today's even stricter environmental regulations require that new munitions and weapon system designs incorporate demilitarization processing issues. Increasingly stringent EPA regulations will not allow the use of OBOD or excessive incineration techniques, so new technologies must be developed to meet the new guidelines.
One type of munition that presents a unique problem for disposal are plastic bonded explosives (PBX) systems. Catalyzed high strength, resilient, and temperature tolerant polymer matrices are utilized by the military in both explosive ordnance as well as in propellants to provide ease in loading and to minimize separation and void formation of the energetic load. These high temperature, high strength, and impact resilient properties of the polymer matrices, which are valued to prevent void formation, are also the same properties that inhibit the efficient removal of the polymer bonded materials from the ordnance during recycling. The polymer materials are sufficiently resilient under normal situations to absorb the impact energy of kinetic removal methods, such as waterjet washout, without reaching the polymer's tensile strengths.
The original formulation of PBX consisted of RDX crystals bound within a polystyrene matrix. The polystyrene coating protected RDX crystals from the intense point stresses and friction experienced during manufacturing and handling, thus preventing premature detonation. This formulation also allowed casting the explosive mixture directly into a warhead. Several variations on the PBX concept arose from the original recipe, however, all formulations are similar in that they consist of an energetic component.
PBX is easily manufactured and can be cast or machined into complicated shapes or injected into small cavities. High mechanical strength, excellent explosive properties, excellent stability, high thermal input insensitivity, and relative insensitivity to handling make PBX the explosive material commonly used in modern weapons systems. The plastic components that give PBX its excellent properties, however, also create a demilitarization problem. For example it is difficult to dissolve these energetic particles that are completely coated in a high molecular weight cross-linked polymer matrix. Among the most popular polymers for PBX formulations are the polyurethanes.
The polyurethane coating on explosive particles in polyurethane-based PBX prevents the direct dissolution of the energetic, or explosive component. Various chemical demilitarization methods have been proposed but none of them have been successful for the recovery of PBX materials. Tompa, et al, (U.S. Pat. No. 4,389,265) and Spencer, et al, (U.S. Pat. No. 5,977,354) used heat to degrade the polymer. Hendry, et al, (U.S. Pat. No. 3,909,497) worked on developing polyurethanes that would preferentially degrade with heat. O'Neill, et al, (U.S. Pat. No. 4,018,636) tried water soluble polymers for PBX in order to aid in the demilitarization of the material. Shaw (U.S. Pat. No. 4,057,442) attempted to use swelling and depolymerizing chemicals to remove the plastic matrix while Heaton, et al, (U.S. Pat. No. 5,538,530) used humic acid and Phillips, et al, (U.S. Pat. No. 6,063,960) used nitric acid to attempt to degrade the polymer and dissolve the explosive. None of these systems have proven practical. Instead, they have proven problematic because they cause excessive degradation of the energetic component and are typically have safety issues because they require the use of excess heat that may lead to autoignition and detonation of the energetic component.
Also, U.S. Pat. Nos 5,363,603 and 5,737,709, which are incorporated herein by reference, teach the use of a fluid jet technology for cutting explosive shells and removing the explosive material, but they do not provide a method for recovering the energetic component, let alone a polymer coated energetic component.
While some of the above methods have met with varying degrees of success, there still remains a need in the art for improved methods and apparatus for demilitarizing plastic bonded explosives in an environmental, efficient and safe manner.